Detection of glaucomatous visual field defects using frequency doubling technology perimetry in a rural hospital

Abstract

To determine the suitability of the Frequency doubling technology perimetry in a rural set up by determining the applicability of the test and the ability of the FOT to identify glaucomatous Visual field losses and to determine a prevalence estimate of Glaucoma using the FOT in Sabatia Eye Hospital, Kenya Using a cross-sectional hospital based design; visual fields were carried out at FEH, Sabatia in rural western Kenya, for a total of 364 eyes of 212 patients between the age of 40 and 93 years. Following the visual field testing with the FOT perimeter, a complete eye examination including lOPs and a detailed funduscopy was carried out on all the patients. A pre-phase to the study was designed at Kenyatta National hospital, Nairobi, which focused on the ability of the FOT to determine the accuracy of detection and localization of scotomas, the time required to perform the test and the compliance o of the patients as compared with the HFA 30-2. At KNH, 47 eyes of 24 patients between the ages of 19 and 83 years were examined and visual fields were performed using the 30-2 HFA and the FOT. Following the visual fields, the eyes were examined and lOP measurements and a careful funduscopy was carried out. The FOT was suitable for a rural set up in Kenya. In 95% of the eyes we were able to perform the screening mode in the first attempt and in 89% we managed to perform the threshold mode in the first attempt. None of the eyes were excluded due to poor reliability indices. The screening mode was found to be more sensitive in detecting glaucomatous field defects than the threshold mode though there were found to be many false positives. The results of the screening mode were reliable in all eyes irrespective of their visual acuity while the results of the threshold mode were reliable in eyes with a visual acuity better than 6/60. The prevalence estimate of glaucoma using the FOTwas 13.46% in FEH, Sabatia. At KNH, the average time taken to perform in the test was the shortest in the FOTscreening mode followed by the threshold mode.The duration was significantly longer

for the HFA 30-2. The patients were compliant in both techniques of testing and the results were reliable. The visual field defects as perceived by the FDT were topographically comparable to the ones found in the HFA. This study found that the performance ability of this test was good in a rural set up in Kenya. In it's current version, the FDT may produce a relatively high number of false positive results due to several confounding factors (poor visual acuity, media opacities, etc.,). However, the FDT perimeter seems generally useful as an adjunct to the clinical diagnosis of glaucoma in a rural setup. It further provides the advantage of being relatively cheap and easy to perform for patients and examiners .